U.S. patent number 4,576,043 [Application Number 06/611,455] was granted by the patent office on 1986-03-18 for methods for metering two-phase flow.
This patent grant is currently assigned to Chevron Research Company. Invention is credited to Tanh V. Nguyen.
United States Patent |
4,576,043 |
Nguyen |
March 18, 1986 |
Methods for metering two-phase flow
Abstract
A method for metering two-phase flow wherein the successive
accelerational pressure drops across an orifice plate and across a
venturi coupled in series with the orifice plate are correlated to
obtain one or more flow-rate parameter.
Inventors: |
Nguyen; Tanh V. (Fullerton,
CA) |
Assignee: |
Chevron Research Company (San
Francisco, CA)
|
Family
ID: |
24449089 |
Appl.
No.: |
06/611,455 |
Filed: |
May 17, 1984 |
Current U.S.
Class: |
73/195; 702/47;
73/861.04; 73/861.52 |
Current CPC
Class: |
G01F
1/74 (20130101) |
Current International
Class: |
G01F
1/74 (20060101); G01F 001/76 (); G01F 001/36 () |
Field of
Search: |
;73/29,195,196,861.04,861.52,861.61,861.63 ;364/510 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Collins et al., "Measurement of Steam Quality in Two-Phase Upflow
with Venturimeters and Orifice Plates", Journal of Basic Eng'g,
Mar. 1971, pp. 11-21. .
Sekoguchi et al., "Two-Phase Flow Measurements with Orifice-Couple
in Horizontal Pipe Line", Bulletin of JSME, vol. 21, No. 162, Dec.
1978, pp. 1757-1761..
|
Primary Examiner: Ruehl; Charles A.
Attorney, Agent or Firm: LaPaglia; S. R. Keeling; E. J.
McGarrigle; P. L.
Claims
What is claimed is:
1. A method for metering two-phase flow in a pipeline comprising
the steps of:
installing a venturi in the pipeline;
coupling an orifice plate in series with the venturi in the
pipeline;
introducing two-phase flow into the pipeline;
measuring the two-phase pressure drop across the venturi;
measuring the two-phase pressure drop across the orifice plate;
and
correlating the two-phase pressure drop across the venturi as
determined by a first set of equations with the two-phase pressure
drop across the orifice plate as determined by a second set of
equations to obtain one or more two-phase flow rate parameters,
wherein said first set of equations comprises: ##EQU8## and wherein
said second set of equations comprises: ##EQU9## where:
1/X=Martinelli's parameter,
x=quality,
.rho..sub.l =the density of a liquid phase,
.rho..sub.g =the density of a gaseous phase,
.DELTA.p=the measured two-phase pressure drop across the device to
which the equation is applied,
C=a correlation coefficient based upon calibration data,
W=the two-phase mass-flow rate,
K=an orifice coefficient for the venturi,
F.sub.p =a flow parameter,
D=the diameter of the orifice,
a=a first constant determined from calibration data, and
b=a second constant based on calibration data.
2. A method for metering two-phase flow in a pipeline comprising
the steps of:
installing a venturi in the pipeline;
coupling an orifice plate in series with the venturi in the
pipeline;
introducing two-phase flow into the pipeline;
measuring the two-phase pressure drop across the venturi;
measuring the two-phase pressure drop across the orifice plate;
and
correlating the two-phase pressure drop across the venturi as
determined by a first set of equations with the two-phase pressure
drop across the orifice plate as determined by a second set of
equations to obtain one or more two-phase flow rate parameters,
wherein said first set of equations comprises: ##EQU10## and
wherein said second set of equations comprises: ##EQU11## where:
1/X=Martinelli's parameter,
x=quality,
.rho..sub.l =the density of a liquid phase,
.rho..sub.g =the density of a gaseous phase,
.DELTA.p=the measured two-phase pressure drop across the device to
which the equation is applied,
C=a correlation coefficient based upon calibration data,
W=the two-phase mass-flow rate,
K=an orifice coefficient for the orifice plate,
F.sub.p =a flow parameter,
D=the diameter of the venturi,
a=a first constant determined from calibration data, and
b=a second constant based on calibration data.
Description
BACKGROUND OF THE INVENTION
The present invention pertains in general to methods for metering
two-phase flow and in particular to methods for metering two-phase
flow using an orifice plate and a venturi in series.
In an oil field in which steam injection is employed to enhance oil
recovery, each of a number of steam injectors may be fed by a
branch of a trunk line from a common steam generator. Due to
flow-splitting phenomena at the branches, a different ratio of
steam to total flow (steam plus water), also called steam quality,
is likely to be present in each branch.
A knowledge of the ratio of steam to total flow being injected in a
two-phase flow is critical to any understanding of the effects of
steam injection. Because it is impractical to predict this ratio
from analysis of the injection apparatus, it is important to be
able to determine flowrate parameters for calculating steam quality
from measurements made at each branch.
Many methods for metering single-phase flow, such as those
dependent upon critical choke flow or those employing single
orifice meters, lose their accuracy when applied to a two-phase
flow system. Other methods, such as steam calorimetry, have
inherent sampling problems.
Two-phase flow may be metered by employing two or more measurements
which are mathematically correlated.
One such approach involves the use of a gamma ray densitometer to
make void fraction measurements and a turbine meter or drag disc to
obtain a second measurement. This approach is limited to a small
quality range and requires the use of an expensive and delicate
gamma ray densitometer instrument.
In another such approach, exemplified by K. Sekoguchi et al,
"Two-Phase Flow Measurements with Orifice Couple in Horizontal Pipe
Line", Bulletin of the ISME, Vol. 21, No. 162, December, 1978, pp.
1757-64, two segmental orifices or baffles are coupled in series.
The pressure drop across each orifice or baffle is measured and
correlated with the pressure drop across the other orifice or
baffle. The orifices must differ in configuration in order to
provide independent measurements for the purpose of correlation.
One drawback of this approach is that data is not presented in
dimensionless form suitable for predicting performances for
different systems.
Yet another such approach involves measurement of a frictional
pressure drop across a twisted tape, measurement of an
accelerational pressure drop across a venturi and correlation of
the results. A disadvantage of this approach is that a very
sensitive device is required to measure the pressure drop across
the twisted tape.
Measurement of the pressure drops across a venturi and an orifice
in series may be done simply and at reasonable cost, as shown in D.
Collins et al, "Measurement of Steam Quality in Two-phase Upflow
with Venturi Meters and Orifice Plates", Journal of Basic
Engineering, Transactions of the ISME, March 1971. Although
concurrent pressure drops were measured for calibration purposes in
Collins et al, pp. 11-21, the pressure drops across an orifice
plate and across a venturi coupled in series have not previously
been correlated for the purpose of metering two-phase flow prior to
the present invention.
SUMMARY OF THE INVENTION
Accordingly, the method of the present invention involves metering
two-phase flow in a pipeline including the following steps. A
venturi is installed in the pipeline. An orifice plate is coupled
in series with the venturi in the pipeline and two-phase flow is
introduced. The respective accelerational pressure drops across the
venturi and across the orifice plate are measured and then
correlated to obtain one or more two-phase flow flowrate
parameters.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view in diagrammatic partial cross-section of an
apparatus for practicing the method according to the present
invention; and
FIG. 2 is a plot of the steam quality as calculated according to
the method of the present invention versus measured steam
quality.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As illustrated in FIG. 1, apparatus for practicing the method
according to the present invention includes an orifice plate 20
having a concentric orifice 25 within a portion of a steam pipeline
10. A venturi 30 is coupled in series with orifice plate 20 so that
the same two-phase flow of steam and water passes through both in
direction 15.
The accelerational pressure drop across orifice plate 20 is
measured by means of pressure gauge 40 while the accelerational
pressure drop across venturi 30 is measured by pressure gauge
50.
Steam pipelines and generators for two-phase steam flow are well
understood by those skilled in the art and will not be discussed
further. Venturi 30 may be a standard Herschel venturimeter.
Orifice plate 20 may be a sharp-edged orifice plate having a
concentric orifice. Gauges 40 and 50 may be piezoelectric
strain-gauges or mercury manometers, for example.
According to a preferred embodiment of the present invention, two
sets of calculations are correlated in order to obtain steam
quality or flow rate. A first set of three equations is applied to
the pressure drop across venturi 30 while a second set of three
equations is applied to the pressure drop across orifice plate
20.
The first set of equations makes use of Martinelli's parameter 1/X
as defined by ##EQU1## where:
X=the steam quality;
.rho..sub.l =the density of the liquid phase (water); and
.rho..sub.g =the density of the gas phase (steam).
Martinelli's parameter is used to calculate the liquid
pseudo-pressure drop, .DELTA.p.sub.l, which is the pressure drop
which would be recorded if the liquid phase were flowing as a
single-phase fluid, so that ##EQU2## where: .DELTA.p=the measured
two-phase pressure drop;
C=a correlation coefficient based upon calibration data; and all
other variables are as defined above.
The liquid pseudo-pressure drop is used to calculate the two-phase
mass flow rate, W, using the equation: ##EQU3## where: K=the
appropriate orifice or venturi coefficient; and all other variables
are as defined above.
In the above set of equations, steam and water densities at given
temperature and pressures are readily available to those skilled in
the art in tabular form. The correlation coefficient, C, is readily
obtainable for a given venturi or orifice by running calibration
tests on the orifice or venturi. The constant, K, may be calculated
according to the American Gas Association Method as described in
"Orifice Metering of Natural Gas", American Gas Association Report
No. 3, June, 1979.
The second set of calculations employs the parameter F.sub.p
modified from Rhodes et al, U.S. Pat. No. 4,312,234, at column 4,
as: ##EQU4## where: D=the diameter of the orifice or venturi, and
all other variables are as defined above.
F.sub.p is correlated as a function of steam quality, x, in the
form:
where a and b are constants obtained by running calibration tests
on a particular orifice or venturi.
The total mass flow rate is then given by: ##EQU5## where all
variables are as defined above.
Accordingly, in order to predict quality and flow rate, equations
(1)-(3) may be applied to orifice plate 20, for example, and
equations (4)-(6) may be applied to venturi 30, for example. These
two sets of equations are solved for the two-phase flow rate, W. At
the correct value for steam quality, x, the two-phase flow rates
given by equations (3) and (6) should be equal.
EXAMPLE
Data was collected using an orifice plate having a 2-inch diameter
orifice and a 2-inch internal diameter venturi tube in a 3-inch
schedule 80-pipe. Two-phase steam was introduced into the pipe.
Equations (1)-(3) were applied to venturi tube 30 and equations
(4)-(6) were applied to orifice plate 20.
For venturi 30, ##EQU6##
For orifice plate 20,
and
As illustrated by the open circles plotted in FIG. 3, the following
results were obtained for steam quality:
______________________________________ Measured Quality Predicted
Quality ______________________________________ 0.75 0.78 0.85 0.88
0.75 0.68 0.65 0.73 0.82 0.78 0.88 0.73 0.77 0.73 0.64 0.63 0.77
0.68 ______________________________________
For comparison, equations (1)-(3) were applied to orifice plate 20
and equation (4)-(6) were applied to venturi 30 as follows:
For venturi 30,
and
For orifice plate 20, ##EQU7##
As illustrated by the triangles plotted in FIG. 3, by applying
equations (1)-(3) to orifice plate 20 and equations (4)-(6) to
venturi 30, the following results were obtained:
______________________________________ Measured Quality Predicted
Quality ______________________________________ 0.75 0.725 0.85
0.675 0.75 0.775 0.65 0.775 0.82 0.725 0.88 0.775 0.77 0.775 0.64
0.623 0.77 0.675 ______________________________________
One of the advantages of the method according to the present
invention is that venturi and orifice plates are very popular in
flow metering and thus are easily obtainable and well understood.
Also, only two parameters are measured to predict flow rates as
opposed to most techniques which require three parameters to be
measured.
While the present invention has been described in terms of a
preferred embodiment, further modifications and improvements will
occur to those skilled in the art. For example, although metering
of two-phase steam has been described above, metering of any
two-phase flow may be obtained by employing the method according to
the present invention.
I desire it to be understood, therefore, that this invention is not
limited to the particular form shown and that I intend in the
appealed claims to cover all such equivalent variations which come
within the scope of the invention as claimed.
* * * * *